Mobile object tracking systems

Abstract

The invention relates to a mobile object tracking system for tracking mobile objects such as vehicles. An array of signpost stations is distributed around an area to be monitored, each signpost station being arranged to transmit a signpost identification signal. An object-based receiver is arranged to receive a signpost identification signal in the event of the object being located within a predetermined distance of a signpost station. An object-based beacon transmitter transmits an object identification signal and an object location signal derived from the signpost identification signal to a central control station via a network of receiver stations. The object is identified and the position of the object is located at the control station on the basis of the object identification and location signals transmitted from the beacon transmitter. The invention extends to a method of tracking mobile objects.

We claim: 
     
       1. A vehicle tracking system comprising: an array of signpost stations distributed strategically and non-uniformly around an area to be monitored, each signpost station being arranged to transmit a signpost identification signal defining a signpost footprint covering at least one route traversed by vehicles, with the signpost footprints of adjacent signpost stations being substantially non-overlapping;   a vehicle-based receiver arranged to receive the signpost identification signal in the event of the vehicle being located within the associated signpost footprint of a signpost station;   a vehicle-based beacon transmitter arranged to transmit a vehicle identification signal and a vehicle location signal derived from the signpost identification signal;   activating means for activating the beacon transmitter in response to unauthorized act being carried out on the vehicle;   a central control station for identifying the vehicle and determining its approximate position on the basis of the vehicle identification and location signals transmitted from the beacon transmitter;   at least one mobile tracking and recovery unit having a position locating unit for homing in on the vehicle once its approximate position has been established; and   a network of receiver stations which is more widespread than the array of signpost stations, each receiver station having receiving means arranged to receive the vehicle identification and location signals originating from the vehicle-based transmitter and transmission means for relaying the signals to the central control station, the receiver stations including position locating means for generating, on the basis of the received vehicle identification signal, and separately of the vehicle location signal, a positional signal relating to the position of the vehicle.   
     
     
       2. A vehicle tracking system according to claim 1 in which remote arming means are provided for selectively arming and disarming the vehicle-based receiver and beacon transmitter. 
     
     
       3. A vehicle tracking system according to claim 1 which includes a short range remote activator for triggering the beacon transmitter, the short range remote activator including entry means for entering various emergency condition codes for transmission to the central control station via the vehicle-based receiver. 
     
     
       4. A vehicle tracking system according to claim 1 in which the vehicle identification signal and the vehicle location signal form a combined signal comprising vehicle identification data, message type data including hijack, normal theft, breakdown and medical emergency data, input status data including door, brake, ignition, boot and bonnet data, signpost data and checking data. 
     
     
       5. A vehicle tracking system according to claim 1 in which the vehicle location signal comprises signpost identification data representative of at least two signpost stations having substantially non-overlapping footprints which have most recently been traversed by the object, and timing data representative of the time lapsed since traversing of the signpost stations. 
     
     
       6. A method of tracking a vehicle comprising the steps of: (a) strategically distributing in an area to be monitored an array of signpost stations having associated signpost footprints defined by a respective signpost identification signal transmitted from a respective associated signpost station, so that each signpost footprint covers at least one route typically traversed by a vehicle, and is substantially non-overlapping relative to signpost footprints of adjacent signpost stations;   (b) transmitting a signpost identification signal from at least one of the signpost stations;   (c) receiving the signpost identification signal at the vehicle in the event of the vehicle moving into the associated signpost footprint of the signpost identification signal;   (d) transmitting from a vehicle-based transmitter a vehicle identification signal and a vehicle location signal derived from the signpost identification signal in the event of an unauthorized act being carried out on the vehicle;   (e) identifying and locating the approximate position of the vehicle on the basis of the vehicle identification and location signal;   (f) tracking and recovering the vehicle by means of at least one mobile tracking unit using the approximate position of the vehicle as a reference;   (g) distributing in the area to be monitored a network of receiver stations which is more widespread than the network of signpost stations, receiving, at one of the receiver stations, the vehicle identification, location and status signals originating from the vehicle-based transmitter;   (h) relaying the vehicle identification, location and status signals to a control station;   (i) monitoring the progress of the vehicle at the control station;   (j) providing, at least some of the receiver stations, position locating means for generating a positional signal on the basis of the vehicle identification signal and independently of the signpost identification signal; and   (k) transmitting the positional and vehicle identification signals to the control station.   
     
     
       7. A method defined in claim 6 wherein the step (c) includes the steps of: accumulating a plurality of different signpost identification signals as the vehicle moves through successive nonoverlapping footprints associated with different signpost stations, and   transmitting the plurality of the signpost identification signals to the central control station for enabling the route of the vehicle to be tracked.   
     
     
       8. A method defined in claim 6 further comprising the steps of entering message type data for receipt at the vehicle and of transmitting from the vehicle message type data in conjunction with the vehicle location and identification signals.